Grounding and indicating device



Dec. 6, 1966 M. 1.. PERRETTA 3,290,668

GROUNDING AND INDICATING DEVICE Filed Aug. 2, 1963 a RED INVENTOR.

MIGHA EL L. PE RRETTA D.EMMETT THOMPSON ATTORNEY.

United States Patent 3,290,668 GROUNDING AND INDICATING DEVICE Michael L. Pcrretta, Kirkviile, N.Y., assignor to (house- Hinds Company, Syracuse, N.Y., a corporation of New York Filed Aug. 2, 1963, Ser. No. 300,714 1 Claim. (Cl. 340-255) This invention relates to and has as a general object a new and improved intrinsically safe and explosion proof operating device, as for example, a grounding and indicating device.

In many locations, it is necessary to discharge an electrostatic charge, and to continuously indicate the fact that a discharge circuit is provided and maintained so that the charge, if any, may be discharged. For example, in bulk tank loading stations for petroleum products, it is necessary to discharge the electrostatic charge present on the individual vehicle tanks prior to and during the time when the tanks are filled with hazardous petroleum products to prevent a discharge spark, or the like from igniting the volatile vapors emanating from the petroleum products. Further, it is necessary to continuously indicate to the loading station operator that the discharge circuit is maintained, and to provide a signal if, for any reason, the discharge circuit is broken.

In such devices, the grounding device includes a grounding clip, which is to be attached to the object intended to be grounded, and the grounding device is provided with a grounding circuit which is energized by the attachment ofvthe grounding clip. The energization of the grounding circuit, in turn, energizes the operating circuit. Because of the hazardous vapors in the atmosphere, the grounding clip must be connected to the device to be grounded by an intrinsically safe circuit, so as to prevent a spark, created by the intentional, or accidental separation of the grounding clip from the object being grounded, from igniting the surrounding atmosphere.

Here-tofore, the operating circuit of prior commercially available devices has been energized by magnetic, or semi-conductor devices in the ground circuit which, by virtue of the energy level at which these devices operate, have prevented these grounding circuits from being intrinsically safe.

Accordingly, it is an object of the invention to provide a new and improved intrinsically safe grounding and indicating device wherein the energizing means for the grounding circuit is achieved through an illuminating means, as opposed to the conventional energizing devices.

More particularly, it is an object of the invention to provide a new and improved intrinsically safe grounding apparatus of the type described, which also functions to indicate the grounding of the vehicle, and which is at the same time explosion proof.

The invention consists in the novel features and constructions and the method hereinafter set forth and claimed.

In describing the invention, reference is had to the accompanying drawings in which like characters designate corresponding parts in all the views.

In the drawings:

FIGURE 1 is a schematic wiring diagram of the p-re ferred embodiment of the invention.

FIGURE 2 is a side elevational view of the apparatus in which the circuit shown in FIGURE 1 is mounted.

Referring to FIGURE 1 of the drawings, the apparatus comprising the preferred embodiment of the invention comprises a grounding clip whichmay be suitably attached in the'conventional manner to the vehicle frame. The clip is connected by a pair of leads 12 and 14 into ICC an explosion proof housing 16, indicated by the dash lines. The housing 16 may be of any suitable type which will function to prevent any flame generated by an explosion therein from escaping to the atmosphere. For example, the box 16 may be of a cast iron construction having a cover which is either threadedly mounted thereon or has a smooth joint of sufficient tolerance and length so that the joint formed by either method is flame quenching.

The leads 14 and 12, which pass into the interior of the box 16 in an explosion proof manner, are connected to a first or ground circuit, generally indicated by the reference numeral 18. This grounding circuit comprises the secondary 20 of a step-down transformer 22, one side of which is connected through a resistor 24 and illumination means comprising a miniature lamp 26, to the lead 14. The opposite side of the transformer secondary 26 is connected to a grounded lead 28 and to the second clip lead 12.

The remainder of the circuit shown in the housing 16 is an operating or test and indicating circuit, and generally indicated by the reference numeral 30, and this circuit serves to test continuously the contact made by the grounding clip 16, and the frame, and to indicate if a proper connection is made between the frame and the clip. The test circuit comprises the primary 32 of the transformer 22 which is connected by lead 34 passing through the housing 16 to the hot side of a volt alternating current supply. The opposite side of the primary 32 of the transformer is connected by lead 36 to the common side of the power supply. Accordingly, it will be seen that the transformer 22 supplies power to the grounding circuit 18, and the transformer 22 is designed so as to operate the grounding circuit at a maximum of 6 volts, and 15 milleamps. Consequently, it will be seen that the ground circuit is intrinsically safe, that is, the current is so low that if the clip 10 should become accidentally separated from the vehicle frame, the energy level of the spark generated by this separation is so low that ignition of any volatile vapors is prevented.

The indicating circuit 30 includes a photo conductive cadmium sulfide cell 38 connected to the common side of the power supply line 4% and 42, a current limiting resistor 44 connected in series with the cell 38, and a sensitive relay 46 connected in the line 42, which in turn is connected by line 48 to the hot side 34 of the power supply. The normally open contact 50 of relay 46 is connected in a series circuit by line 40 through a load relay 52 to line 48 so that upon closure of the contact 50, relay 52 is energized. Load relay 52 comprises a pair of fixed contacts 54 and 56 and a movable contact 58. Contact 54 is connected by line 60, line 62 through a green indicating light 64, the opposite side of which is connected by line 66 to the hot side of the power supply 34. Contact 56 is connected by line 68 to a red indicating light 70, the opposite side of which is connected by line 72 and line 66 to the hot line 34. The center contact 58 of relay 52 is normally in engagement with the contact 56 and completes a circuit from line 36 through line 74 which is connected to the center contact 58 to contact 56 and through the red "light 70, by the circuit just described, to normally energize the red lamp '70. This is to normally indicate to the o-perator of the filling station that the grounding clip is not attached to the vehicle frame, and hence to prevent him from commencing the filling operation.

After the grounding clip 10 has been securely attached to the vehicle frame, the ground circuit is completed so as to energize the lamp 26. This will cause the cadmium sulfide cell 38 to conduct current in turn completing the circuit through the relay 46 to energize the relay. The

energization of relay 46 causes the contact 50 to close, thus energizing load relay 52. The load relay 52, upon energization, will cause the contact 58 to move away from the contact 56, and into engagement with the contact 54, thus breaking the circuit and de-energizing the red lamp 70. Upon engagement of the contacts 58 and 54, the circuit will be completed for the energization of the lamp 64, thus indicating to the operator that the clip 10 has been properly attached to the vehicle frame.

At this point, a control circuit is completed from the hot line 34, through lines 66 and 72, to line 76, which is connected through a valve or pump, schematically indicated by the box 80, to line 82, which is, in turn, connected by line 60 and contacts 54 and 58, line 74 to the common side of the power supply at line 36, thus energizing the valve or pump 80, and permitting the loading station operator to fill the vehicle with the petroleum product.

The values of the resistor 24 and lamp 26 in grounding circuit 18 are selected so that the lamp 26 will not become energized, unless the resistance of the ground circuit 18 is of 100 ohms, or less. Accordingly, if there is no contact between the clip 10 and the vehicle frame, or improper contact, the red lamp 70 will remain energized, and the valve or pump 80 will remain de-energized, thus indicating to the operator that a proper ground connection has not been made and preventing operation of the filling apparatus.

As will be obvious, therefore, the arrangement is of the fail-safe variety, in that if the clip 10 becomes disconnected from the frame during the filling operation, the red light 70 will be energized, and the valve or pump 80 de-energized, thus halting filling operation until a proper ground contact has been reestablished.

Referring to FIGURE 2, it will be seen that the housing 16 is provided with a cover 84 which is fastened to the housing by means of a plurality of bolts 86. The joint between the cover 84 and the body housing 16 is a ground joint of suflicient length and sufficiently close tolerance so as to provide a flame quenching path from the interior of the housing to the atmosphere surrounding the housing. The lamps 64 and 70 are mounted in lamp carrying means 88 and 90, respectively, and these mounting means are also explosionproof. The fitting 92 and 94 are combination drain and breather devices of the type commercially available and serve to prevent and drain off any condensation or moisture from the interior of the housing. A conduit 93, which is part of a grounded conduit system, is threadedly connected to the righthand end of the housing and carries the power leads 34 and 36 and valve control or pump leads 82 and 76, while the fitting 98 is an explosion-proof connecting fitting to connect the leads 12 and 14 carried in cable 100 to the jaws 102 and 104 of the grounding clip 10.

Finally, the grounded leg 28 of the grounding circuit 18 is connected to the housing -16, which in turn is part of the grounded conduit system, as above set forth. Accordingly, it will be seen that the entire unit is explosionproof in that the power leads 34 and 36 are connected to the housing 16 by means of the threaded connection between the conduit 96 and the housing 16 and the indicating lamps 64 and 70 are carried in the explosionproof fittings 88 and 90. As pointed out previously, 'howewn h lea 1 e sw r s? went t s accumulating an electrostatic charge.

a low level as to make the device intrinsically safe since any spark occurring between the clip and the vehicle frame is of insufficient energy level to ignite combustible gases present in the surrounding atmosphere.

It will be apparent, therefore, that the invention provides an intrinsically safe grounding circuit which will not operate unless a proper ground contact is made, and that the testing, or indicating circuit, is located in an explosion proof housing, thus rendering the complete arrangement explosion proof. Further, the design is of a simple and economical type, which is reliable in operation. I

While the preferred embodiment of the invention has been disclosed by way of example in conjunction with a tank filling station for bulk petroleum products wherein combustible mixtures of gases are present in the atmosphere, it is to be understood that the invention may be used in any location where such combustible gas mixtures may be present in the atmosphere and where it is desirable to ground apparatus which is capable of For example, the apparatus comprising the preferred embodiment of the invention could be adapted for use in a hospital operating room to ground and continuously indicate the grounding of any apparatus in the operating room utilizing electric power. Further, it is to be understood that the control circuit which has been shown in the disclosure as operating a valve or pump, or the like, may be utilized as a control circuit for any desired purpose. Accordingly, the scope of the invention is intended to be limited only by the appended claim.

What I claim is:

An explosion proof ground indicating device comprising an explosion proof housing, a power supply in said housing, a first relay circuit connected to said power supply, said circuit including a relay and a light sensitive cell connected in series, a second relay circuit connected to said power supply and including a load relay connected in series through the contacts of said first relay for energization upon energization of said first relay, signal indicating means connected through the contacts of said second relay for indicating whether said second relay is-energized, or de-energized, an intrinsically safe low energy non-inductive circuit having a portion extending exteriorly of said housing, a grounding clip having conducting jaws for attachment to an object to be grounded, a low energy consuming lamp mounted in said housing in juxtaposition to said light sensitive cell and operable when energized to render said cell conductive for the energization of said first relay, said lamp being connected in series with the jaws of said clip whereby, when said clip is attached to a metallic object to be ground, said lamp is energized and one side of said low energy non-inductive circuit being connected to ground.

References Cited by the Examiner UNITED STATES PATENTS 2,275,833 3/1942 Adams 3l7-l24 X 2,276,338 3/1942 Potter et a1. 317-124 X 3,040,211 6/1962 Caldwell 317-2 3,149,319 9/1964 Messmer et al. 317l24 X NEIL C. READ, Primary Examiner.

MYER, Assistant E camirter, 

